On the basis of a population balance and the kinetic mechanism of free-radical suspension polymerization, a mathematical model of the suspension polymerization process is proposed. The population balance model which describes a mechanism involving the particle size distribution (PSD) in disperse systems leads to an integrodifferential equation. The basic numerical approach of this work is to use the finite-difference-differential technique with the logarithmic scale for particle size. The problem then was reduced to obtaining the numerical solution of a set of nonlinear ordinary differential equations. The numerical solutions were compared to experimental data, such as the reaction conversion which includes the gel effect and the particle size distributions, to yield the model parameters by Marquardt＇s method. The regression demonstrates reasonably good accuracy.